Chirally Functionalized Hollow Nanospheres Containing L‐Prolinamide: Synthesis and Asymmetric Catalysis

Abstract

Chirally functionalized hollow nanospheres with different surface properties were successfully synthesized by co-condensation of (2S,1'R,2'R)-N-tert-butyloxycarbonylpyrrolidine-2-carboxylic acid [2'-(4-trimethoxysilylbenzylamide)cyclohexyl] amide with 1,2-bis(trimethoxysilyl)ethane or tetramethoxysilane using F127 (EO(106)PO(70)EO(106)) as surfactant in water. The TEM and N(2) sorption characterizations show that the particle size of the hollow nanosphere is 15-21 nm with a core diameter of 10-16 nm. These L-prolinamide-functionalized hollow nanospheres are highly efficient solid catalysts for the direct asymmetric aldol reaction between cyclohexanone and aromatic aldehydes. It was found that the addition of water in the reaction system not only enhanced the catalytic activity but also increased the enantioselectivity, which is probably due to the enhanced hydrogen bond between the amide oxygen atom and the hydroxyl group of water. Moreover, the catalytic activity increases sharply as the surface hydrophobicity of the hollow nanospheres increases. These hollow nanospheres are quite stable and can be reused with almost the same enantioselectivity and only a slight decrease in catalytic activity.

Synthesis and Catalytic Application of Hollow Silica Nanospheres

“…Yang et al developed the general methods to fabricate HSNs based on F127-NaH 2 PO 4 -Na 2 HPO 4 and F127-TMB systems (F127: EO 106 PO 70 EO 106 ; TMB: mesitylene). [31][32][33][34][35][36][37] The assembly of the silicate species around the corona of individual micelle results in the formation of nanospheres with a hollow interior after removal of the surfactant by extraction or calcination. The particle size of the HSNs is in the range of 12-30 nm.…”

An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

“…Among the silica fibers, spheres, rods and nanoparticles, the hollow nanospheres are very attractive, given that the hollow interior can encapsulate the guest molecules for wide application potentials [19][20][21][22][23][24][25][26][27][28]. The modification of the shell of the hollow nanospheres may further expand the application potentials of the hollow nanospheres [29][30][31][32][33][34][35]. The strategies for the synthesis of hollow silica-based nanospheres were already well reviewed [36,37], and can be categorized as: selective etching or dissolution, soft templating, self templating, galvanic replacement method, and Ostwald ripening method, etc.…”

Surface‐Passivated SBA‐15‐Supported Gold Nanoparticles: Highly Improved Catalytic Activity and Selectivity toward Hydrophobic Substrates

“…[13] Recently, we also found that the catalytic activity of a chiral prolinamide catalyst that was supported on hollow nanospheres increased sharply with increasing surface hydrophobicity after surface passivation. [17] The surface passivation of a silica-supported BINOLÀTi (BINOL = 1,1'-bi-2-naphthol) catalytic system has been used to afford highly efficient catalysts. [18][19][20][21][22] Chen and co-workers prepared a new type of superhydrophobic material, in which a Co-incorporated SiO 2 nanocomposite was functionalized with organic groups, by surface passivation.…”